Marine Boilers Safety Devices (Alarms and Trips)

Alarms and trips boiler

Safety of machineries and its equipments are vital on board ship. Many accidents have occurred in the past related to boiler system on board ship. So to make its operation risk free, a numerous Alarms and trips are fitted on the boiler system. Various alarms and trips installed on boiler system on board are given below:

Important Alarms and Trips on Marine Boilers

Functions Audible and Visual Actions
1) Low water level Alarm
2) Low low water level Alarm and Trip Burner stop
3)High water level Alarm
4) High high water level Alarm and Trip Feed water pump stop
5) Low steam pressure Alarm
6) High steam pressure Alarm and Trip Burner stop
7) Low feed-water pressure Alarm Stand-by pump start
8) Low fuel oil pressure Alarm Stand-by pump start
9) Low fuel oil temperature Alarm
10) High fuel oil temperature Alarm
11) Low combustion air pressure Alarm and Trip Burner stop
12) Low atomizing steam pressure Alarm and Trip Burner stop
13) Flame failure Alarm and Trip Burner stop
14) Burner not in firing position Alarm and Trip Burner stop
Boiler On ship

©2011, Author: jblevine2004, Source: Flickr , | CC-BY-SA |

Explanation of each Alarm and Trips and why they occur:

1) Low water level: Since boiler is converting water into Steam, therefore the consumption of water is taking place, if the level is not monitored manually, a stage will occur where water level will drop to a certain level(L2) and alarm will be seen and heard.

2) Low low water level: If alarm at level L2 is not acknowledged the level will drop further to level L1, and burner will stop firing to prevent boiler shell from damage due to excessive heat from burner flame.

3) High water level : Alarm will sound when consumption of water does not matches the intake of feed water via feed water pump. Water has reached level H1.

4) High high water level : If water at level H1 is not acknowledged, the feed water pump will stop at level H2, therefore cutting water supply to the boiler drum, the feed pump stop to prevent the drum of boiler from excessive hydraulic pressure exerted by the feed water, which may explode the boiler drum(at-least weaken it).

5) Low steam Pressure : this Alarm occurs to show various cases such as burner is not firing up-to the mark, feed water is less in the boiler therefore less pressure.

6) High steam pressure : Alarm with Trip to burner occur to prevent the damage to the steam drum due to excessive pressure of the steam.

7) Low feed-water pressure : Due to certain problem the feed-pump#1 is having problem to generate ample pressure to push the water inside the boiler drum, therefore stand-by feed-pump starts to maintain the pressure of feed-water. (Remember there is a feed check valve between feed-water pump and drum.)

8) low F.O. pressure : The pump to boost the F.O pressure for injection is not generating enough pressure due to myriad reasons, therefore a stand-by fuel oil pump is started to supplement for the loss in pressure, this occur because when fuel is being injected into the furnace. it should have ample pressure so that the fuel can atomize completely.

9) Low fuel oil temperature : Low fuel temperature lead to a large amount of sunburned fuel accumulation in the furnace and there is high probability of explosion

10) High F.O temperature : Since the F.O should be within favorable temperature condition, Heating up of oil give off Alarm.

11) Low combustion air pressure : F.D fans (Force Draft fans) are used to supply combustion air to the boiler burner for complete combustion, but when there is alarm for low combustion air pressure, it should be seen that there is no damage to the fan blades and there is no obstruction to the intake of combustion air.

12) Low atomizing steam pressure : where steam is used as the atomizing medium this trip will occurs if any obstruction is in the hole of the steam supply, or the pipeline supplying the steam.

13) Flame Failure : [NOTE: This is Overridden during starting up/firing up of the boiler] This trip occurs to prevent the accumulation of fuel into the furnace, which may become the source of explosion if not correctly purged.

14) Burner not in firing position : since the burner is not in firing position, one case maybe because the arc is not striking up between the electrode and there’s the supply of fuel, so to prevent the accumulation and explosion, this trip is initiated.

Note :Feel free to comment down below if i miss any alarms and trips or made any mistake.

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  1. Pabitra Kumar Behera

    Is there anything difference of mounting between main boiler and auxiliary boiler?

    1. admin

      No other than their set limits value ( Main and Auxiliary Boiler have different working pressure ) there is no change between the mountings fitted on main boiler or on auxiliary boiler. In large main boilers with super heated stem there is additional safeties installed for that part.

  2. Pabitra Kumar Behera

    Thank u sir for your respond


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